Occasionally water trapped beneath the surface catastrophically flooded across the surface, carving huge channels up to 100 kilometers wide, 1 kilometer deep, and thousands of kilometers long. The floods left long mesas and teardrop-shaped islands, such as those in Ares Vallis. The floods emptied into the northern lowlands, possibly creating short-lived seas. Viking Orbiter image of Ares Vallis, courtesy of NASA and the Jet Propulsion Laboratory.